1. Field of Invention
The invention relates to a belt device that supports an endless belt with a support roller so as to run, and an image forming apparatus provided with the belt device.
2. Description of Related Art
There exists an image forming apparatus that includes a belt device that transports a recording medium on an endless belt inside the image forming apparatus. As disclosed in, for example, Japanese Laid-Open Patent Publication No. 2001-163424, a belt device includes a protrusion that is provided on an inner surface of an endless belt. The protrusion extends along a running direction of the endless belt to prevent the endless belt from being out of position while the endless belt is running.
However, in the belt device, the protrusion formed on the endless belt runs onto a support roller supporting the endless belt while the endless belt is running. To solve such a problem, the belt device disclosed in Japanese Laid-Open Patent Publication No. 2001-163424 includes a rotating member that has a tapered surface and is disposed concentrically with the support roller and is provided between the protrusion and the support roller. As the tapered surface of the rotating member contacts the protrusion, meandering of the endless belt is restricted and the protrusion is prevented from running onto the support roller.
In the belt device, meandering of the endless belt while the belt is running under normal conditions is restricted by the rotating member having the tapered surface. However, when an external force is applied to the endless belt, the protrusion runs onto the rotating member along the tapered surface of the rotating member while the rotating member is being rotated. Thus, the protrusion readily runs onto the rotating member.